Question

Tìm x, biết 

a) x²=5 

b) 3x²-12=0 

c) 4x²-3=-9 

d) 5x²-3=-3 

Answer 1

\(a,x^2=5\Leftrightarrow x=\pm\sqrt{5}\)

Vậy \(S=\left\{\pm\sqrt{5}\right\}\)

\(b,3x^2-12=0\Leftrightarrow3x^2=12\Leftrightarrow x^2=4\Leftrightarrow x=\pm2\)

Vậy \(S=\left\{\pm2\right\}\)

\(c,4x^2-3=-9\)

\(\Leftrightarrow4x^2=-6\)

\(\Leftrightarrow x^2=-\dfrac{3}{2}\) (loại)

Vậy pt vô nghiệm.

\(d,5x^2-3=-3\)

\(\Leftrightarrow5x^2=0\)

\(\Leftrightarrow x=0\)

Vậy \(S=\left\{0\right\}\)

Answer 2

a)

`x^2 =5`
`=>\(\left[{}\begin{matrix}x=\sqrt{5}\\x=-\sqrt{5}\end{matrix}\right.\)

b)

`3x^2 -12=0`

`<=>3x^2 =12`

`<=>x^2 =4`

\(< =>\left[{}\begin{matrix}x=2\\x=-2\end{matrix}\right.\)

c)

`4x^2 -3=-9`

`<=>4x^2 =-6`

`<=>x^2 =-3/2` (vô lí vì `x>=0AA x` )

d)

`5x^2 -3=3`

`<=>5x^2 =0`

`<=>x^2 =0`

`<=>x=0`